CN111164780B

CN111164780B - Organic light emitting diode display, organic light emitting diode pixel and display

Info

Publication number: CN111164780B
Application number: CN201880063011.0A
Authority: CN
Inventors: C-Y·陆; 刘睿; L·蔡
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2017-09-28
Filing date: 2018-09-24
Publication date: 2022-12-09
Anticipated expiration: 2038-09-24
Also published as: CN111164780A; WO2019067365A1; US20200388652A1; US11164911B2

Abstract

The display may have an array of pixels formed of organic light emitting diodes and thin film transistor circuits. The organic light emitting diode may be interposed between the substrate (30) and the cover layer (70). The organic light emitting diode may be a white light emitting diode (26) that emits white light that is filtered by a color filter array (76) to produce colored light. The color filter array may be located above or below the array of light emitting diodes. A microcavity may be formed between the substrate (30) and each light emitting diode (26). The microcavity may be formed by an anode (36) in the light emitting diode and first and second layers (78) having different indices of refraction. The low refractive index layer may be formed by color filters in the color filter array. Light from the light emitting diodes may resonate within the microcavity under each light emitting diode before exiting the display as colored light.

Description

Organic light emitting diode display, organic light emitting diode pixel and display

This application claims priority to U.S. provisional patent application 62/564,732, filed on 28.9.2017, which is hereby incorporated by reference in its entirety.

Background

The present invention relates generally to electronic devices having displays, and more particularly to electronic devices having organic light emitting diode displays.

Electronic devices typically include a display. Displays such as organic light emitting diode displays include an array of pixels that emit light to display an image for a user. Pixels of a display may include different color sub-pixels to provide the display with the ability to display color images. The organic light emitting diode is controlled by a thin film transistor circuit.

It can be challenging to implement high resolution displays with organic light emitting diode pixels. Displays sometimes use white organic light emitting diodes with red, green and blue color filters to achieve higher resolution. However, if care is not taken, a display having a white organic light emitting diode may not exhibit the desired level of optical performance.

It would therefore be desirable to provide an improved organic light emitting diode display.

Disclosure of Invention

The display may have an array of pixels on a substrate. The display may be an organic light emitting diode display and the pixels may comprise organic light emitting diodes of different colors. The display may include thin film transistor circuitry that controls the organic light emitting diode pixels.

The organic light emitting diode may be interposed between a substrate and a cover layer (cover layer). The organic light emitting diode may be a white light emitting diode that emits white light, which is filtered by a color filter array to generate colored light. The color filter array may be located above or below the array of light emitting diodes.

A microcavity may be formed between the substrate and each of the light emitting diodes. The microcavity may be formed by an anode of the light emitting diode and first and second layers having different refractive indices. In one illustrative arrangement, a color filter array is located below the light emitting diode array and serves as a low index layer in the microcavity. Light from the leds may resonate within the microcavity beneath each led to pass through the color filter multiple times before exiting the display as colored light.

In another suitable arrangement, a color filter array is located above the array of light emitting diodes, and an oxide layer is used as a low refractive index layer in the microcavity under each light emitting diode.

The white light emitting diode may be formed of an emission layer that mixes primary colors or complementary colors to generate white light, may be formed of a plurality of emission layers that mix primary colors or complementary colors to generate white light, may be formed of an emission layer and a phosphor that collectively generate white light, or may be formed of a plurality of light emitting diode units that are stacked in series (tandem) and connected in series to generate white light.

Drawings

FIG. 1 is a perspective view of an exemplary electronic device with a display in accordance with one embodiment.

FIG. 2 is a schematic diagram of an exemplary electronic device with a display, according to one embodiment.

Fig. 3 is a top view of an exemplary display in an electronic device according to one embodiment.

FIG. 4 is a cross-sectional side view of a portion of an exemplary organic light emitting diode display, according to one embodiment.

Fig. 5 is a cross-sectional side view of an exemplary white organic light emitting diode having a single emissive layer, according to one embodiment.

Fig. 6 is a cross-sectional side view of an exemplary white organic light emitting diode having two emissive layers, according to one embodiment.

Fig. 7 is a cross-sectional side view of an exemplary white organic light emitting diode having three emissive layers, according to one embodiment.

Fig. 8 is a cross-sectional side view of an exemplary white organic light emitting diode having an emissive layer and a phosphor according to one embodiment.

Fig. 9 is a cross-sectional side view of an exemplary white organic light emitting diode having first and second stacked light emitting diode units coupled in series according to one embodiment.

Fig. 10 is a cross-sectional side view of an exemplary white organic light emitting diode having first, second, and third stacked light emitting diode units coupled in series according to one embodiment.

Fig. 11 is a cross-sectional side view of an exemplary pixel with a white organic light emitting diode with a bottom color filter forming part of a microcavity, according to one embodiment.

Fig. 12 is a cross-sectional side view of an illustrative pixel with a white organic light emitting diode having a top color filter and a second microcavity in accordance with an embodiment.

Detailed Description

An illustrative electronic device of the type that may be provided with a display is shown in fig. 1. The electronic device 10 may be a computing device such as a laptop computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wristwatch device, a hanging device, a headset or earpiece device, a device embedded in eyeglasses or other apparatus worn on the user's head, or other wearable or miniature device, a computer monitor or other display containing an embedded computer or other electronic apparatus, a computer display or other monitor not containing an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which the electronic apparatus with a display is installed in a kiosk or automobile, an apparatus that implements the functionality of two or more of these devices, or other electronic apparatus. In the illustrative configuration of fig. 1, device 10 is a portable device, such as a cellular telephone, media player, tablet, wrist device, or other portable computing device. Other configurations may be used for the device 10, if desired. The example of fig. 1 is merely illustrative.

In the example of fig. 1, device 10 includes a display, such as display 14 mounted in housing 12. The housing 12, which may sometimes be referred to as a shell or case, may be formed from plastic, glass, ceramic, fiber composite, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. The housing 12 may be formed using a unitary configuration in which a portion or all of the housing 12 is machined or molded as a single structure, or may be formed using multiple structures (e.g., an internal frame structure, one or more structures forming an external housing surface, etc.).

Display 14 may be a touch screen display incorporating conductive capacitive touch sensor electrode layers or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a non-touch sensitive display. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. Touch sensors can be formed using electrodes or other structures on a display layer containing the pixel array or on a separate touch panel layer attached (e.g., using an adhesive) to the pixel array.

Display 14 may include an array of pixels formed from Liquid Crystal Display (LCD) components, an electrophoretic pixel array, a plasma pixel array, an organic light emitting diode pixel array or other light emitting diodes, an electrowetting pixel array, or pixels based on other display technologies. Configurations in which display 14 is an organic light emitting diode display are sometimes described herein as examples. The use of organic light emitting diode pixels to form the display 14 is merely illustrative. In general, display 14 may be formed using any suitable type of pixels.

A display cover layer such as a transparent glass layer or a light-transmissive plastic layer may be used to protect the display 14. An opening may be formed in the display cover layer. For example, openings may be formed in the display cover layer to accommodate buttons, speaker ports, or other components. Openings may be formed in housing 12 to form communication ports (e.g., audio jacks, digital data ports, etc.), to form openings for buttons, etc.

Fig. 2 is a schematic diagram of the apparatus 10. As shown in fig. 2, the electronic device 10 may have a control circuit 16. Control circuitry 16 may include storage and processing circuitry to support operation of device 10. The storage and processing circuitry may include storage devices, such as hard disk drive storage devices, non-volatile memory (e.g., flash memory or other electrically programmable read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random access memory), and so forth. Processing circuitry in control circuitry 16 may be used to control the operation of device 10. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, and the like.

Input-output circuitry in device 10, such as input-output device 18, may be used to allow data to be provided to device 10, and to allow data to be provided from device 10 to external devices. The input-output devices 18 may include buttons, joysticks, scroll wheels, touch pads, keypads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light emitting diodes and other status indicators, data ports, and the like. A user may control the operation of device 10 by supplying commands through input-output device 18 and may receive status information and other output from device 10 using output resources of input-output device 18. The input-output devices 18 may include one or more displays, such as the display 14.

The control circuitry 16 may be used to run software, such as operating system code and applications, on the device 10. During operation of device 10, software running on control circuitry 16 may display images on display 14 using an array of pixels in display 14.

Display 14 may have a rectangular shape (i.e., display 14 may have a rectangular footprint and a rectangular perimeter edge extending around the rectangular footprint) or may have other suitable shapes. The display 14 may be planar or may have a curved profile.

A top view of a portion of display 14 is shown in fig. 3. As shown in FIG. 3, display 14 may have an array of pixels 22. The pixels 22 may receive data signals through signal paths such as data lines D and may receive one or more control signals through control signal paths such as horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.). There may be any suitable number of rows and columns of pixels 22 in display 14 (e.g., ten or more, a hundred or more, or a thousand or more). Each pixel 22 may have a light emitting diode 26 that emits light 80 under the control of a pixel control circuit formed from transistor circuitry, such as thin film transistor 58 and thin film capacitor. Transistor 58 may be a polysilicon thin film transistor, a semiconductor oxide thin film transistor (such as an indium gallium zinc oxide transistor), or a transistor formed from other semiconductors.

Display 14 may include pixels (sometimes referred to as subpixels) of different colors. For example, the display 14 may include red, green, and blue pixels, or may include pixels of other colors. In one exemplary arrangement, the color pixels 22 in the display 14 may be formed using light emitting diodes that emit light of a desired color. For example, red, green, and blue pixels may be formed by depositing red, green, and blue organic light emitting materials side by side on a substrate. With this type of arrangement, each light emitting diode 26 emits colored light, such as red, blue, or green light.

In another suitable configuration, the color pixels 22 in the display 14 may be formed using white organic light emitting diodes that emit white light that is filtered by a color filter such as the color filter 76 to produce colored light. Color filter 76 may be formed from a colored polymer deposited and patterned to form a color filter array. For example, the red pixel 22 may be formed of a white organic light emitting diode paired with the red color filter 76R, the green pixel 22 may be formed of a white organic light emitting diode paired with the green color filter 76G, and the blue pixel 22 may be formed of a white organic light emitting diode paired with the blue color filter 76B. Display 14 may include pixels of other colors, if desired. Arrangements that pair white organic light emitting diodes with red, green, and blue color filters are sometimes described herein as examples.

A cross-sectional side view of a portion of an exemplary organic light emitting diode display near one of the light emitting diodes 26 is shown in fig. 4. As shown in fig. 4, display 14 may include a substrate layer, such as substrate layer 30. The substrate 30 may be formed of a polymer, glass, sapphire, a semiconductor material such as silicon, or other suitable material.

Thin film transistor circuitry 44 may be formed on substrate 30. Thin film transistor circuitry 44 may include layer 32. Layer 32 may include inorganic layers such as inorganic buffer layers, barrier layers (e.g., barrier layers to moisture and impurities), gate insulators, passivation layers, interlayer dielectrics, and other inorganic dielectric layers. Layer 32 may also include an organic dielectric layer, such as a polymer planarization layer. Metal layers and semiconductor layers may also be included in layer 32. For example, a semiconductor such as silicon, a semiconductor oxide semiconductor, or other semiconductor material may be used to form the semiconductor channel region of thin film transistor 58 (fig. 3). Metals in layer 32, such as metal traces 74, may be used to form transistor gate terminals, transistor source-drain terminals, capacitor electrodes, and metal interconnects.

As shown in fig. 4, the light emitting diode 26 may be formed within an opening in the pixel defining layer 60. The pixel defining layer 60 may be formed of a patterned photoimageable polymer, such as polyimide, and/or may be formed of one or more inorganic layers, such as silicon nitride, silicon dioxide, or other suitable materials.

Each light emitting diode 26 may include a light emitting diode layer 38 interposed between a respective anode 36 and cathode 42. The anode 36 may be patterned from a metal layer (e.g., silver, aluminum, or other suitable metal) and/or one or more other conductive layers, such as a layer of indium tin oxide (ito), molybdenum oxide (MoOx), titanium nitride (TiNx), or other transparent conductive material. In one exemplary arrangement, anode 36 can be formed from one or more layers of a non-conductive material (e.g., silicon oxide (SiOx), silicon nitride (SiNx), or a polymer) having a top layer of a conductive transparent material (e.g., indium tin oxide, indium gallium zinc oxide, other transparent conductive oxides, etc.) and a bottom layer of a reflective metal (e.g., silver, aluminum, a compound of a reflective metal, etc.). The cathode 42 may be formed from a common conductive layer deposited on top of the pixel defining layer 60. The cathode 42 may be formed from a thin metal layer (e.g., a metal layer such as a magnesium silver layer) and/or indium tin oxide or other transparent conductive material. The cathode 42 is preferably sufficiently transparent to allow light 80 to exit the light emitting diode 26.

The example of fig. 4 is merely illustrative, where the anode of diode 26 is formed from a patterned conductive layer and the cathode of diode 26 is formed from a blanket conductive layer. Anode 36 may be formed from a blanket conductive layer and cathode 42 may be formed from a blanket conductive layer, if desired.

The example of fig. 4 is merely illustrative, where the diode 26 is a "top-emitting" organic light emitting diode. The display 14 may be implemented using bottom emitting organic light emitting diodes, if desired.

Metal interconnect structures may be used to interconnect transistors and other components in circuitry 44. The metal interconnect lines may also be used to route signals to capacitors, to data lines D and gate lines G, to contact pads (e.g., contact pads coupled to gate driver circuitry), and to other circuitry in display 14. As shown in fig. 4, layer 32 may include one or more patterned metal layers for forming interconnects such as metal traces 74 (e.g., traces 74 may be used to form data lines D, gate lines G, power supply lines, clock signal lines, and other signal lines).

Display 14 may have a protective outer display layer, such as cover layer 70, if desired. The outer display layer may be formed of a material such as sapphire, glass, plastic, transparent ceramic, or other transparent material. A protective layer 46 may cover the cathode 42. Layer 46, which may sometimes be referred to as a thin film encapsulation layer, may include a moisture resistant structure, an encapsulant material such as a polymer, an adhesive, and/or other materials to help protect the thin film transistor circuitry.

Functional layer 68 may be interposed between layer 46 and cover layer 70. The functional layers 68 may include touch sensor layers, circular polarizer layers, and other layers. The circular polarizer layer may help reduce light reflection from reflective structures such as anode 36 and cathode 42. The touch sensor layer can be formed from an array of capacitive touch sensor electrodes on a flexible polymer substrate. The touch sensor layer may be used to collect touch input from a user's finger, a stylus, or from other external objects. An optically clear adhesive layer may be used to attach a cover layer 70 (e.g., a layer of glass, sapphire, polymer, or other suitable material) and a functional layer 68 to underlying display layers such as layer 46, thin-film transistor circuitry 44, and substrate 30.

Light-emitting diode layer 38 may include organic light-emitting layers (e.g., a red light-emitting layer in red diodes 26 that emit red light, a green light-emitting layer in green diodes 26 that emit green light, and a blue light-emitting layer in blue diodes 26 that emit blue light, a combination of white light-emitting materials, etc.). The light emitting material may be a material such as a phosphorescent material or a fluorescent material, which emits light during operation of the diode. The light-emitting material in light-emitting diode layer 38 may be sandwiched between additional diode layers, such as a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer.

As discussed in connection with fig. 3, the pixel 22 may include a white organic light emitting diode 26 that emits white light that is filtered by a color filter to produce colored light. The color filter 76 (fig. 3) may be located below the light emitting diode 26 (e.g., between the substrate 30 and the diode 26) or may be located above the light emitting diode 26 (e.g., between the overcoat layer 70 and the diode 26).

The white emission of the organic light emitting diode 26 of fig. 4 can be achieved using one or more emissive layers and/or one or more phosphor layers to mix three primary colors (e.g., red, green, and blue) or two complementary colors (e.g., yellow/orange and blue). Fig. 5-10 illustrate various examples of structures that may be used to form white light emitting diodes 26 of display 14.

As shown in FIG. 5, the white light emitting diode 26 may include a light emitting diode layer 38 sandwiched between an anode 36 and a cathode 42. Light-emitting diode layer 38 includes an electron transport layer 48, an emissive layer 50, a hole transport layer 52, and a hole injection layer 54.

In the example of fig. 5, the white light emitting diode 26 includes a single emissive layer 50 that mixes different colored emissive materials to produce white light 80W. For example, the emissive layer 50 may be a mixture of primary color emissive materials, such as red, green, and blue emissive materials, that combine to form the white light 80W, or the emissive layer 50 may be a mixture of complementary color emissive materials, such as blue and yellow (or orange) emissive materials, that combine to form the white light 80W.

In the example of fig. 6, the emissive layer 50 of the white light emitting diode 26 includes a first emissive layer 50-1 and a second emissive layer 50-2. Emissive layer 50-1 and emissive layer 50-2 may be complementary color emissive materials that combine to form white light 80W (e.g., layer 50-1 may be a blue emissive material and layer 50-2 may be a yellow or orange emissive material, or vice versa), or one of emissive layer 50-1 and emissive layer 50-2 may include a mixture of two primary color emissive materials and the other emissive layer may include a third primary color emissive material that combine to form white light 80W (e.g., layer 50-1 may be a blue emissive material and layer 50-2 may be a mixture of red and green emissive materials, or vice versa).

In the example of fig. 6, the emissive layers 50 of the white light emitting diode 26 include a first emissive layer 50-1, a second emissive layer 50-2, and a third emissive layer 50-3. The emission layers 50-1, 50-2, and 50-2 may be primary color emission materials that combine to form white light 80W. For example, layer 50-1 may be a blue emissive material, layer 50-2 may be a green emissive material, and layer 50-3 may be a red emissive material. This ordering of layers is merely illustrative. In general, the red, green, and blue emitting layers in layer 50 of diode 26 may be stacked in any suitable order.

In the example of fig. 8, white light 80W is formed by pairing emissive layer 50 with a phosphor layer, such as phosphor layer 56. The phosphor layer 56 may be formed on the substrate 30 (e.g., the phosphor 56 may be formed under the substrate 30, as shown in the example of fig. 8, over the substrate 30, over the emissive layer 50, or in other suitable locations in the diode 26). Emissive layer 50 and phosphor layer 56 may produce light of a complementary color that combines to form white light 80W. For example, the emissive layer 50 may emit blue light, and the phosphor 56 may be a yellow phosphor. Some of the blue photons from the blue emissive layer 50 will be emitted from the diode 26 without being altered to form blue light. Other blue photons from the blue emissive layer 50 will be converted to yellow light by the yellow phosphor layer 56. The blue light and the yellow light may combine to form white light 80W. The use of a blue emitting material and a yellow phosphor is merely illustrative. If desired, the emissive layer 50 can emit ultraviolet light and/or the phosphor layer 56 can emit green and/or red light.

In the example of FIG. 9, white light 80W is formed from a pair of LED units 38-1 and 38-2 stacked in series. Light emitting diode unit 38-1 includes electron transport layer 48-1, emissive layer 50-1, hole transport layer 52-1, and hole injection layer 54-1. Light emitting diode unit 38-2 includes electron transport layer 48-2, emissive layer 50-2, hole transport layer 52-2, and hole injection layer 54-2. The led units 38-1 and 38-2 may emit light of complementary colors (e.g., blue and yellow or other suitable complementary colors) that combine to form white light 80W. For example, emissive layer 50-1 may emit blue light and emissive layer 50-2 may emit yellow light, or vice versa.

The led cells 38-1 and 38-2 may be electrically connected in series. A charge generation interconnect layer, such as charge generation layer 62, may be located between cells 38-1 and 38-2 and may be used to couple cell 38-1 to cell 38-2. The charge generation layer 62 may be formed of, for example, an n-type layer (sometimes referred to as an electron injection conductive layer) and a p-type layer (sometimes referred to as a hole injection conductive layer).

In the example of FIG. 10, white light 80W is formed from three LED units 38-1, 38-2, and 38-3 stacked in series. Light emitting diode unit 38-1 includes electron transport layer 48-1, emissive layer 50-1, hole transport layer 52-1, and hole injection layer 54-1. Light emitting diode unit 38-2 includes electron transport layer 48-2, emissive layer 50-2, hole transport layer 52-2, and hole injection layer 54-2. Light emitting diode unit 38-3 includes an electron transport layer 48-3, an emissive layer 50-3, a hole transport layer 52-3, and a hole injection layer 54-3. Light emitting diode units 38-1, 38-2, and 38-3 may emit primary colors of light (e.g., red, green, and blue light) that combine to form white light 80W. For example, emission layer 50-1 may emit blue light, emission layer 50-2 may emit green light, and emission layer 50-3 may emit red light. This ordering of the units is merely illustrative. In general, the red, green, and blue light-emitting units 38-1, 38-2, and 38-3 may be stacked in any suitable order.

The LED units 38-1, 38-2 and 38-3 may be electrically connected in series. A first charge-generating interconnect layer, such as charge-generating layer 62-1, may be located between cells 38-1 and 38-2 and may be used to couple cell 38-1 to cell 38-2. A second charge generation interconnect layer, such as charge generation layer 62-2, may be located between cells 38-2 and 38-3 and may be used to couple cell 38-2 to cell 38-3. The charge generation layers 62-1 and 62-2 may each be formed of an n-type layer (sometimes referred to as an electron injection conductive layer) and a p-type layer (sometimes referred to as a hole injection conductive layer).

In displays where white light is filtered through color filters to form color pixels, care must be taken to avoid loss of light source efficiency, color filter alignment errors, and color shift at wide viewing angles. Fig. 11 and 12 show illustrative arrangements for forming color pixels 22 using white light emitting diodes and color filters with improved optical efficiency, reduced alignment error, and minimal color shift over wide viewing angles.

In the example of FIG. 11, pixels 22 of display 14 include white light emitting diodes 26 and color filters, such as color filter 76. The white light emitting diode 26 may be formed using one of the arrangements of fig. 5-10, or may be formed using other light emitting diode structures. The color filter 76 may be a red color filter, a green color filter, a blue color filter, or other suitable color filters. Color filters 76 may be formed on a high index of refraction material such as layer 78. Layer 78 may be formed of titanium dioxide, silicon nitride, silicon oxide, or other suitable inorganic material having a relatively high refractive index. A reflective layer, such as reflective layer 84, may be formed on substrate 30 below light emitting diodes 26 to reflect light upward and out of display 14.

A capping layer such as capping layer 64 may be formed on the cathode 42. Capping layer 64 may be an organic layer that helps to increase the transmission through cathode 42. Barrier layer 92 may include organic layers such as organic layer 72 (e.g., manganese or other suitable organic material) and inorganic layers such as inorganic layers 66 and 74 (e.g., silicon nitride, silicon oxide, or other suitable inorganic material). Additional layers such as those described in connection with fig. 4 may be used in display 14. For example, the layer 102 may include the protective layer 46 and/or the functional layer 68 (fig. 4). The cover layer 70 may cover the organic light emitting diode 26.

Reflective materials such as metals and reflective interfaces (e.g., an interface between a high index of refraction material and a low index of refraction material) may cause light to resonate within the pixel 22. For example,

electrodes

42 and 36 may be at least partially reflective and may exhibit a similar effect as a microresonator having parallel mirrors, sometimes referred to as a microcavity (e.g., a Fabry Perot interferometer). The spectral emission of a pixel 22 may depend on the resonator characteristics of the microcavity (or microcavities) within the pixel 22. The optical efficiency of the pixel increases when constructive interference occurs between the incident light and the reflected light in the microcavity. The microcavity effect can be optimized by adjusting the thickness of the layers in the pixel 22 and/or by selecting certain materials to achieve the desired resonance effect (e.g., selecting materials with different refractive indices, different levels of reflectivity, etc.).

The pixel 22 may include one or more microcavities that increase the optical efficiency of the pixel. A first microcavity may be formed between the anode 36 and the cathode 42 (as shown by resonant light 94), a second microcavity may be formed between the barrier layer 92 (as shown by resonant light 96), and a third microcavity may be formed between the anode 36 and the high refractive index layer 78 (as shown by light 98). These microcavities can be tuned to optimize the optical efficiency of the pixel 22.

During operation, white light from diode 26 resonates in the microcavity within pixel 22 and is filtered by color filter 76 to produce colored light 80C. The microcavity formed by anode 36, color filter layer 76 and high index layer 78 may serve a variety of purposes. First, the difference in refractive index between color filter layer 76 (e.g., a low refractive index material such as a polymer) and high refractive index layer 78 causes light 98 to resonate within

layers

76 and 78, resulting in constructive interference and thus improved optical efficiency and better viewing angle performance. The difference in refractive index between

layers

78 and 76 may be 0.4, 0.5, 0.6, 0.8, 1, greater than 1, or less than 1. Second, this microcavity effect means that light 98 passes through color filter 76 multiple times before exiting pixel 22 as colored light 80C. Because the light 98 passes through the color filter 76 multiple times, the color filter 76 may be relatively thin. A thin color filter layer may in turn reduce unwanted absorption in the pixels 22.

In addition, the color filter 76 of fig. 11 is formed under the light emitting diode 26, and thus may allow greater flexibility in the type of deposition method used to deposit the color filter material 76 on the substrate 30. For example, layer 88 may be formed using a thin film transistor array process, and layer 90 may be formed by an organic light emitting diode and thin film encapsulation process. Because layer 88 is formed on substrate 30 before organic light-emitting diode layer 38, color filters (e.g., red, green, and blue color filters) may be deposited on substrate 30 using photolithography techniques, fine metal mask techniques, or other techniques without risk of damaging organic light-emitting diode layer 38.

However, this is merely illustrative. If desired, a color filter layer 76 may be formed over the light emitting diodes 26. An example of this type of arrangement is shown in figure 12.

As shown in fig. 12, the pixels 22 of the display 14 include a white light emitting diode 26 and a color filter such as color filter 76. The white light emitting diode 26 may be formed using one of the arrangements of fig. 5-10, or may be formed using other light emitting diode structures. The color filter 76 may be a red color filter, a green color filter, a blue color filter, or other suitable color filters. Color filter 76 may be formed on barrier layer 92. A reflective layer, such as reflective layer 84, may be formed on substrate 30 below light emitting diodes 26 to reflect light upward and out of display 14.

Additional layers such as those described in connection with fig. 4 may be used in display 14. For example, the layer 102 may include the protective layer 46 and/or the functional layer 68 (fig. 4). The cover layer 70 may cover the organic light emitting diode 26.

A capping layer such as capping layer 64 may be formed on cathode 42. Capping layer 64 may be an organic layer that helps to increase the transmission through cathode 42. Barrier layer 92 may include organic layers such as organic layer 72 (e.g., manganese or other suitable organic material) and inorganic layers such as inorganic layers 66 and 74 (e.g., silicon nitride, silicon oxide, or other suitable inorganic material).

The pixel 22 may include one or more microcavities that increase the optical efficiency of the pixel. A first microcavity may be formed between the anode 36 and the cathode 42 (as shown by the resonating light 94), a second microcavity may be formed between the barrier layers 92 (as shown by the resonating light 96), and a third microcavity may be formed between the anode 36 and the high refractive index layer 78 (as shown by the light 98). The low refractive index layer 86 may be formed of an inorganic layer (e.g., an oxide material or other inorganic material) or an organic layer (e.g., a polymer material or other organic material). The high refractive index layer 78 may be formed of titanium dioxide, silicon nitride, silicon oxide, or other suitable inorganic material having a relatively high refractive index. The difference in refractive index between

layers

78 and 86 may be 0.4, 0.5, 0.6, 0.8, 1, greater than 1, or less than 1. The microcavity in the pixel 22 can be adjusted to optimize the optical efficiency of the pixel 22.

During operation, white light from diode 26 resonates in the microcavity within pixel 22 and is filtered by color filter 76 to produce colored light 80C. The difference in refractive index between the low index layer 86 and the high index layer 78 causes light 98 to resonate within the

layers

86 and 78, resulting in constructive interference and thus improved optical efficiency and better viewing angle performance.

According to one embodiment, there is provided an organic light emitting diode display including a substrate, an overcoat layer, a white organic light emitting diode interposed between the substrate and the overcoat layer, and a color filter interposed between the white organic light emitting diode and the substrate.

According to another embodiment, an organic light emitting diode display includes a high refractive index layer interposed between a substrate and a color filter.

According to another embodiment, an organic light emitting diode display includes a reflective layer interposed between a high refractive index layer and a substrate.

According to another embodiment, the reflective layer comprises a metal.

According to another embodiment, the high refractive index layer comprises a material selected from titanium dioxide and silicon nitride.

According to another embodiment, a white organic light emitting diode includes an anode, and the anode, high refractive index layer, and color filter form a microcavity that resonates light from the light emitting diode between the high refractive index layer and the anode.

According to another embodiment, a white organic light emitting diode includes an emission layer that mixes three primary colors to form white light.

According to another embodiment, a white organic light emitting diode includes a plurality of emissive layers that each emit light of an associated color, and the light from the plurality of emissive layers combines to form white light.

According to another embodiment, a white organic light emitting diode includes a blue emission layer that emits blue light and a phosphor that converts some of the blue light to yellow light and the blue light and the yellow light combine to form white light.

According to another embodiment, a white organic light emitting diode includes at least two light emitting diode units stacked in series and coupled in series.

According to one embodiment, there is provided an organic light emitting diode pixel including a substrate, a white organic light emitting diode on the substrate, the white organic light emitting diode including an anode, a cover layer formed over the white organic light emitting diode, and a first layer having a first refractive index and a second layer having a second refractive index higher than the first refractive index, the first layer and the second layer being interposed between the white organic light emitting diode and the substrate, the anode, the first layer and the second layer forming a microcavity, and light from the white organic light emitting diode resonating within the microcavity.

According to another embodiment, the organic light emitting diode pixel includes a color filter interposed between the overcoat layer and the white organic light emitting diode.

According to another embodiment, the first layer comprises a color filter layer.

According to another embodiment, an organic light emitting diode pixel includes a metal reflector interposed between the second layer and the substrate.

According to another embodiment, an organic light emitting diode pixel includes a capping layer interposed between the capping layer and the white organic light emitting diode.

According to one embodiment, a display is provided that includes a substrate, an organic light emitting diode array on the substrate that emits white light, a color filter array that filters the white light to produce colored light, an overcoat layer over the organic light emitting diode array, the colored light passing through the overcoat layer; and a microcavity between each organic light emitting diode and the substrate, at least some of the white light resonating in the microcavity before passing through the cover layer as colored light.

According to another embodiment, the microcavity is formed from first and second layers having different refractive indices.

According to another embodiment, the first layer of the microcavity is formed by a portion of the color filter array.

According to another embodiment, a display includes a metal reflector interposed between a microcavity and a substrate.

According to another embodiment, a display includes a capping layer interposed between an organic light emitting diode array and a cover layer.

The foregoing is merely exemplary and various modifications may be made by those skilled in the art without departing from the scope and spirit of the embodiments. The foregoing embodiments may be implemented independently or in any combination.

Claims

1. An organic light emitting diode display comprising:

a substrate;

a cover layer;

a white organic light emitting diode interposed between the substrate and the cover layer; and

a color filter interposed between the white organic light emitting diode and the substrate; and

a layer interposed between the substrate and the color filter, wherein the layer has a refractive index higher than that of the color filter,

wherein a difference in refractive index between the layer and the color filter causes light from the light emitting diode to resonate between the layer and the color filter.

2. The organic light-emitting diode display defined in claim 1 further comprising a reflective layer interposed between the layer and the substrate.

3. The organic light-emitting diode display defined in claim 2 wherein the reflective layer comprises a metal.

4. The organic light-emitting diode display defined in claim 3 wherein the layer comprises a material selected from the group consisting of titanium dioxide and silicon nitride.

5. The organic light-emitting diode display defined in claim 1 wherein the white organic light-emitting diode comprises an anode and wherein the anode, the layers and the color filter form a microcavity that resonates light from the light-emitting diode between the layers and the anode.

6. The organic light-emitting diode display defined in claim 1 wherein the white organic light-emitting diode includes an emissive layer that mixes three primary colors to form white light.

7. The organic light-emitting diode display defined in claim 1 wherein the white organic light-emitting diode comprises a plurality of emissive layers that each emit light of an associated color and wherein light from the plurality of emissive layers combines to form white light.

8. The organic light-emitting diode display defined in claim 1 wherein the white organic light-emitting diode comprises a blue-emitting layer that emits blue light and a phosphor that converts some of the blue light to yellow light and wherein the blue light and the yellow light combine to form white light.

9. The organic light-emitting diode display defined in claim 1 wherein the white organic light-emitting diode includes at least two light-emitting diode units that are stacked in series and coupled in series.

10. An organic light emitting diode pixel, comprising:

a substrate;

a white organic light emitting diode on the substrate, wherein the white organic light emitting diode includes an anode;

a cover layer formed over the white organic light emitting diode; and

a first layer having a first refractive index and a second layer having a second refractive index higher than the first refractive index, wherein the first layer and the second layer are interposed between the white organic light emitting diode and the substrate, wherein the second layer is interposed between the substrate and the first layer, wherein the anode, the first layer, and the second layer form a microcavity, wherein light from the white organic light emitting diode resonates within the microcavity, and wherein the first layer includes a color filter layer.

11. An organic light emitting diode pixel according to claim 10, further comprising a metal reflector interposed between the second layer and the substrate.

12. The organic light emitting diode pixel of claim 10, further comprising a capping layer interposed between the capping layer and the white organic light emitting diode.

13. A display, comprising:

a substrate;

an organic light emitting diode array on the substrate, the organic light emitting diode array emitting white light;

a color filter array that filters the white light to produce colored light;

a cover layer over the organic light emitting diode array, wherein the colored light passes through the cover layer; and

a microcavity located between each organic light emitting diode and the substrate, wherein at least some of the white light resonates in the microcavity before passing through the cover layer as colored light, wherein the microcavity is formed from first and second layers having different refractive indices, and wherein the first layer of the microcavity is formed from a portion of the color filter array.

14. The display of claim 13, further comprising a metal reflector interposed between the microcavity and the substrate.

15. The display defined in claim 14 further comprising a capping layer interposed between the organic light-emitting diode array and the capping layer.